Hand tool with magnetic brake

ABSTRACT

A hand tool having a motor-operated shaft that drives a saw, the motor being rendered operable when pressure is applied to a trigger while a tool-manipulating handle is being grasped. Said tool is provided with a magnetic brake that comprises an electromagnetic coil affixed to the housing of the tool and an armature normally biased away from the coil carried by and rotatable with the shaft, the coil remaining de-energized during operation of the shaft and saw. Said actuator, upon release of the trigger, shifting a switch to cause de-energization of the motor and energization of the electro-magnetic coil to produce a magnetic field effective on the armature to draw it into braking engagement with a brake lining provided adjacent the coil.

United States Patent 1151 3,703,654

Karubian 1 Nov. 21, 1972 [54] HAND TOOL WITH MAGNETIC 3,335,304 8/1967 'Brongersma ..310/77 BRAKE 2,809,309 10/1957 Evans ..310/77 [72] Inventor: Ralph Karubian, 2001 West Gage Avenue, Los Angeles, Calif. 90047 Filed: June 30, 1971 Appl. No.: 158,268

US. Cl, .i ..3l0/77, 310/50, 143/17 C,

Int. Cl. ..H02k 7/10 Field of Search ..3l0/47, 50,77, 74, 75, 76, 310/66, 68, 68 D, 92, 93; 200/16 A, 157; 143/17 C; 30/167 References Cited UNITED STATES PATENTS 3/1957 Mowery ..143/17 C Deuschle ..310/77 Primary Examiner-R. Skudy Attorney-Hyman Jackman 57 ABSTRACT A hand tool having a motor-operated shaft that drives a saw, themotor being rendered operable when pressure is applied to a trigger while a tool-manipulating handleis being grasped. Said tool is provided with a magnetic brake that comprises an electro-magnetic coil affixed to the housing of the tool and an armature normally biased away from the coil carried by and rotatable with the shaft, the coil remaining de-energized during operation of the shaft and saw. Said actuator, upon release of the trigger, shifting a switch to cause de-energization of the motor and energization of the electro-magnetic coil to produce a magnetic field effective on'the armature to draw it into braking engagement with a brake lining provided adjacent the coil.

5 Claims, 5 Drawing Figures PKTENTEBNMI I972 SHEET 1 OF 2 l 2% Mm L QMERUM 7 NM INVENTOR. RALPH KIPUB/AA/ P'ATEN'TEflnnvel m2 sum 2 OF 2 INVENTOR. KARI/WAN EAL PH 1. HAND .TOOL WITH MAGNETIC BRAKE BACKGROUND OF INVENTION 1. Field of the Invention -Whilehaving a wide application of use, the invention is most useful on tools having high speed saws or cutters that, due to the nature of their use, are largely exposed. Carcass-splitting saws of the type used in abottoirs are examples of hand tools that are apt to cause injury to the hands of the user, not only because of the slippery environment of use but because of the long over-run of saws after the power has been shut-off. Also, power tools that are hand manipulated may be large, heavy and unwieldy, and depending on the resistance generated in the kerf of the saw, may cause the operator to lose control. Effecting quick stoppage of saw rotation will greatly increase safety of use.

Brief description of the prior art: The applicant, a manufacturer of a varied line of carcass-splitting power saws, has no knowledge of braking means of the nature disclosed in this application. For various reasons, prior attempts to provide such saws with brakes for their cutters have failed. Some of the reasons are increase in unwieldiness, increased cost of manufacture, slowness of braking action, etc.

SUMMARY OF THE INVENTION The invention comprises an electrically operated magnetic brake that is applied to the motor-driven shaft that rotates a high-speed saw. A trigger of a tool of the type referred to, when pressed, closes the motor AC circuitto drive the shaft, and when released, opens the motor circuit and closes a rectified DC circuit to the electro-magnetic coil of said brake to create a magnetic field that attracts an armature carried by the shaft, bringing said shaft and the saw to arapid stop. The AC electric current input is the circuit that is rectified. The above is arranged so the trigger may be rapidly pressed and released so the operator may control the saw in a manner that will minimize overheating and, also, minimize shorts and break-downs.

An object of the invention isto provide a power tool as characterized herein that has the usual trigger conno] for operating said tool, and includes automatic control effective upon release of the trigger to stop operation of the tool.

Another object of the invention is to provide such a tool with a single AC power source and to automatically effect a rectification of such AC to DC for operating a magnetic brake to stop tool operation instantly upon release of the trigger.

This invention also has for its objects to provide such means that are positive in operation, convenient in use, easily installed in a working position and easily disconnected therefrom, economical of manufacture, relatively simple, and of general superiority and serviceability.

The invention also comprises novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description, which is based on the accompanying drawings. However, said drawings merely show, and the following specification merely describes one embodiment of the present invention, which is given by way of illustration or example only.

In the drawings, like reference characters designate similar parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a broken side elevational view of'a tool in I the form of a carcass-splitting saw provided with a magnetic, operation-stopping brake and control means therefor.

FIG. 2 is an enlarged fragmentary sectional view I DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The tool that is used as the basis for the present invention, best seen in FIGS. 1 and 3, comprises an elongated body having an-enlarged housing 11 rearwardly of said body, a motor shell l2for a motor 13, a rear handle 14 extending from the housing 12, and a laterally extending handle 15 on the body 10, that cooperates with handle 14 for steadying the tool in operation while being suspended by a hanger 16 from a counterweighted hanger cable. A rear guard 17 on the forward endof the body 10 protects the hand holding the handle l5from the sawblade 18 which, by a pair of bevel gears 19, is driven by the shaft 20. The latter, by means of a coupling 21, is connected to and rotates with the motor shaft 22 (FIGS. 3 and 4). The portion of the rear handle 14 that is connected to and encloses the rear end of the motor shell 12 is enlarged to form a housing 23 that is closed by a cover 24. The trigger 25 is pivoted at 26 so it may be squeezed by the fingers of the hand gripping the handle 14 whereby the nose 27 of said trigger moves in a direction to actuate the hereinafter described operating components of the tool.

The above tool, in the usual manner, is provided with a power cable 28 to supply-AC to the motor 13 housed in the shell 12. In this instance, the usual switch that is closed by the nose 27 of the trigger 25 has been replaced by a double-pole, single-throw microswitch 29.

The improvements of the present invention comprise, generally, said microc-switch 29, an actuator 30-,

a spring 31 that biases said actuator in a direction to retain the motor-controlling pole of the switch open, a rectifier 32 in the form of a solid state power supply converter, a magnetic brake 33 located withinthe body 10, an AC line circuit 34 inter-connecting the motor 13, microswitch 29 and the input of the rectifier 32, a DC circuit 35 connecting the output of said rectifier with the coil 36 of thebrake 33, and a member 37 to mount the armature 38.

As shown in FIG. 2, the actuator 30 comprises a lever on a fulcrum39, with an end 40 biased by spring 31 in a direction toward the nose 27 of the trigger 25, and an opposite end 41 that is biased by said spring 31 to depress the switch button 42 which mounts a bridging contact 43 that normally bridges one pair of pole contacts 44 under bias of a spring 45, and bridges a second pair of pole contacts 46 when spring 45 is compressed under pressure applied to the trigger 25 through lever 30;

The rectifier or converter 32 is a common device that changes the AC of Circuit 34 to the DC of circuit 35 suitable to energize the electric-magnetic coil 36. As an example, the rectifier converts conventional 110 V. AC that energizes the motor 13 to 90 V. DC.

The coil 36 of the brake 33 is shown in FIG. 3 as being housed in an encapsulating ring 47 that is affixed to a transverse wall 48 of the enlarged portion of housing 11, the forward face of the ring 47 being enclosed by a friction or brake lining 49 that is backed up by the coil 36. v

The armature 38 is shown as a circular magnetizable, preferably paramagnetic disc that is mounted on the member 37 and is capable of moving only longitudinally on a serrated or notched enlargement 50 thereof, toward and from the friction lining 49. A flat spring 51 has a central hole, the edge of which is engaged in a groove 52 of member 37. Said spring is provided with flexible arms 53 that are connected by cap screws 54 to edge-adjacent spring portions of the armature. Said arms 53 are biased to normally retain the armature in spaced relation to the friction lining 49, as shown in FIG. 3.

OPERATION The tool is connected for operation, to circuit 34 by means of any suitable on and off starter switch. With more the tool held by its handles 14 and 15, the trigger is pressed to cause its nose 27 to press on the lever end 40,- compress the spring 31 and moreethe lever end 41 in a direction to release the switch button 42, allowing the spring 45 in switch 29 to open the normally closed pole 46 and close the normally .open pole contacts 44. The circuit 34 to the motor 13 will be closed and the latter energized to drive shaft and rotate the saw blade 34. The pole contacts 44, being open, the circuit to the rectifier 32 is open, the brake 33, therefore, being non-operating.

Upon release of the trigger, the spring 31 will return the lever 30 to the position of FIG. 2, causing compression of spring 45 so the bar 43 bridges the pole contacts 46, thereby connecting the circuit 34 to the input of the rectifier and, simultaneously, opening the, motoroperating circuit. As a result, the conversion of the AC of circuit 34 by said rectifier to the DC of circuit 35 will cause energization of the electromagnetic coil 36 and generation of a magnetic field that attracts the armature 38. The latter, against the light flexure of the spring arms 53, will be drawn into frictional engagement with the friction disc 49. Since, as explained, the

armature is keyed to and turns with the shaft 20, the rotation of the latter will be broken, causing the saw blade 34 to stop its rotation.

It will be clear that with the trigger in released position, the motor 13 and the parts driven thereby remain inactive, irrespective whether the mentioned starter switch is on or off.

While the foregoing illustrates and describes what is now contemplated to be the best mode of carrying out the invention with respect to both the method and apparatus, the same is, of course, subject to modification without departing from the spirit and scope of the invention.

Having thus described the invention, what is claimed an? desired toge secured by etters Pate t is:

.' In a ban power too aving an e ectric motor driven by an electric circuit powered by an A.C. line, and a cutter-operated shaft driven by said motor, said tool being provided with a trigger which, when pressed, closes said motor circuit, the improvement comprising:

a. a magnetic brake having an electromagnetic coil fixed to the tool with and fixedly mounting a friction member, and an armature carried by and engaged to be rotational with the motor shaft and disposed in the field of said coil, said friction member being disposed between said coil and armature,

b. a double-pole, single-throw switch, one pole of which is in circuit with said motor and the other pole is in the line only, i

c. spring-biased actuating means when un-actuated, interengaging the trigger and the switch to close the motor-energizing pole and A.C. circuit, and when actuated by the trigger to close the brake coil 'D.C. circuit to cause magnetic attraction of the armature and the coil and frictional engagement of a face of the former and the friction member. v

2. In a hand tool according to claim 1, the shaft being provided with an enlargement on which the armature is slidably and non-rotationally mounted.

3. In a hand tool according to claim 2, a flat spring member mounted on the shaft enlargement and provided with a plurality of flexible portions that are affixed to the face of the armature opposite to the face that engages the friction member.

4. In a hand tool according to claim 1 in which the double-pole, single-throw switch has the mentioned motor-energizing pole normally closed, and the coilenergizing pole normally open, and the actuating means including a biasing spring to open the normally closed pole and close the normally open pole when the trigger is unactivated whereby activating of the trigger will restore the switch poles to their initial conditions.

5. In a hand tool according to claim 2 in which the spring-biased actuating means comprises a lever having its end that is engaged with the trigger biased by the spring to move said lever end and the trigger to nonoperated position. 

1. In a hand power tool having an electric motor driven by an electric circuit powered by an A.C. line, and a cutter-operated shaft driven by said motor, said tool being provided with a trigger which, when pressed, closes said motor circuit, the improvement comprising: a. a magnetic brake having an electromagnetic coil fixed to the tool with and fixedly mounting a friction member, and an armature carried by and engaged to be rotational with the motor shaft and disposed in the field of said coil, said friction member being disposed between said coil and armature, b. a double-pole, single-throw switch, one pole of which is in circuit with said motor and the other pole is in the line only, c. spring-biased actuating means when un-actuated, interengaging the trigger and the switch to close the motor-energizing pole and A.C. circuit, and when actuated by the trigger to close the brake coil D.C. circuit to cause magnetic attraction of the armature and the coil and frictional engagement of a face of the former and the friction member.
 1. In a hand power tool having an electric motor driven by an electric circuit powered by an A.C. line, and a cutter-operated shaft driven by said motor, said tool being provided with a trigger which, when pressed, closes said motor circuit, the improvement comprising: a. a magnetic brake having an electromagnetic coil fixed to the tool with and fixedly mounting a friction member, and an armature carried by and engaged to be rotational with the motor shaft and disposed in the field of said coil, said friction member being disposed between said coil and armature, b. a double-pole, single-throw switch, one pole of which is in circuit with said motor and the other pole is in the line only, c. spring-biased actuating means when un-actuated, interengaging the trigger and the switch to close the motorenergizing pole and A.C. circuit, and when actuated by the trigger to close the brake coil D.C. circuit to cause magnetic attraction of the armature and the coil and frictional engagement of a face of the former and the friction member.
 2. In a hand tool according to claim 1, the shaft being provided with an enlargement on which the armature is slidably and non-rotationally mounted.
 3. In a hand tool according to claim 2, a flat spring member mounted on the shaft enlargement and provided with a plurality of flexible portions that are affixed to the face of the armature opposite to the face that engages the friction member.
 4. In a hand tool according to claim 1 in which the double-pole, single-throw switch has the mentioned motor-energizing pole normally closed, and the coil-energizing pole normally open, and the actuating means including a biasing spring to open the normally closed pole and close the normally open pole when the trigger is unactivated whereby activating of the trigger will restore the switch poles to their initial conditions. 